Archived posting to the Leica Users Group, 2000/03/01

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Subject: Re: [Leica] apo definitions
From: "Jacques Bilinski" <jbilin@axionet.com>
Date: Wed, 1 Mar 2000 20:38:02 -0800

> The
> definition tells us that a lens is apochromatically corrected if
> three wavelengths  are brought to the same focus. But in optical
> design we discuss errors in fractions of microns. Now if three colors
> have a focal difference of one tenth of a micron, do we then accept
> this as being "the same focus". (?)
>
If three colors have a focal difference of one tenth of a micron would it
not then be likely that  3 (slightly other) colors have *exactly* the same
focus (within a tolerance of zero microns)? If one plots the focus location
as a function of frequency (colour) and this curve oscillates such that 3
different colours have the same focus then would this not fit this
definition of apochromatic?